When an IS-2000 mobile station (MS) requests a dormant mode handoff to a new base site controller (BSC) for a packet data call, an IS-2000 traffic channel is allocated for the handoff. A traffic channel is needed when the MS or packet data serving node (PDSN) have new data to transmit. A traffic channel Is also required for Point-to-Point Protocol (PPP) connection and Mobile IP registration procedures when the dormant mode handoff requires a change in the serving PDSN.
In IS-2001 the establishment of a traffic channel for the MS requires a transport layer connection, a Signaling Connection Control Part (SCCP) connection, to first be established between the mobile switching center (MSC) and the BSC targeted in the handoff. The traffic channel and connection are established by way of the following IS- 2001 message exchange between the BSC and MSC:
1. Upon reception of an IS-2000 Origination message, the target BSC sends a CM Service Request message to the MSC. The CM Service Request message includes the mobile's authentication and registration parameters and is encapsulated in a SCCP Connection Request message.
2. The MSC responds with an Assignment Request message to the BSC to request wireless resources for the handoff. This message is normally sent after successful authentication and authorization of the MS. The Assignment Request message is encapsulated in an SCCP Connection Confirm message (or a DTI message if an SCCP Connection Confirm message was previously sent and the SCCP connection was established). An SCCP connection now exists for the call.
3. Upon successful establishment of an A10/A11 connection between the serving PDSN and new PCF, the BSC may send an Assignment Failure (in SCCP DT1) message to the MSC to indicate that assignment of radio resource was not completed. When this message is sent, it is sent not because the traffic channel assignment procedure failed, but because the BSC has determined that a traffic channel is not required for this particular dormant mode handoff. This would occur when there is no data to be transmitted or when the serving PDSN does not change.
4. The MSC sends a Clear Command (in SCCP DT1) message to the BSC requesting release of dedicated resources for the call.
5. The BSC responds with a Clear Complete (in SCCP DT1) message to the MSC acknowledging release of dedicated resources for the call. The MSC subsequently releases the SCCP connection for the call. MSC and BS exchange SCCP RLSD (released) and SCCP RLC (release completed).
The message exchange above illustrates what IS-2001-A currently requires of the BSC and MSC even though the dormant mode packet data handoff did not actually need a traffic channel. A messaging solution that more efficiently addresses dormant mode handoffs when a traffic channel is not needed would make MSC/BSC communication more efficient and conserve communication resources. Thus, there is a need for a method and apparatus to more efficiently facilitate dormant mode, packet data mobile handoffs.